1. Field of the Invention
The present invention relates to an inkjet image forming apparatus for forming an image on a sheet by ejecting an ink onto the sheet.
2. Description of the Related Art
Heretofore, there has been widely known an inkjet image forming apparatus for forming an image on a sheet by ejecting an ink onto the sheet from an inkjet head, based on image information read out or transmitted from the other device. The inkjet image forming apparatus is generally built-in with an endless transport belt at a predetermined position opposing to the inkjet head to transport a sheet. The image forming apparatus is operable to form an image on a sheet by ejecting an ink from the inkjet head onto the sheet being transported by the transport belt.
In the inkjet image forming apparatus, in view of likelihood that the ink ejected from the inkjet head may adhere to the transport belt and smear the transport belt, it is an ordinary practice to clean the transport belt by contacting an absorbent member having absorbed a cleaning liquid with the transport belt, as disclosed in e.g. Japanese Unexamined Patent Publication No. 2006-264174 (prior art D1) and Japanese Unexamined Patent Publication No. 2004-196505 (prior art D2).
Prior art D1 relates to a technology of cleaning a transport belt, wherein a cleaning liquid is periodically supplied to an absorbent member, considering likelihood that a large frictional force may be generated between the transport belt and the absorbent member due to shortage of the cleaning liquid absorbed in the absorbent member, and consequently driving of the transport belt may be unstable. Prior Art D2 discloses that purified water is used as a cleaning liquid.
A cleaning liquid for use in cleaning a transport belt may evaporate, considering that the cleaning liquid is a solution. For instance, evaporation rate of the cleaning liquid is different depending on environmental conditions such as the ambient temperature, the ambient humidity, or the air flowing velocity in the image forming apparatus. Prior art D1 and D2 do not consider the abovementioned matter. Accordingly, in the case where the cleaning liquid is used in a condition that the cleaning liquid is relatively less likely to evaporate, the cleaning liquid may be excessively fed to the transport belt despite that the transport belt is sufficiently wet with the cleaning liquid. This may cause waste of the cleaning liquid. On the other hand, in the case where the cleaning liquid is used in a condition that the cleaning liquid is relatively highly likely to evaporate, feeding of the cleaning liquid to the transport belt may be insufficient despite that the transport belt is dry. This may cause unstable driving of the transport belt resulting from an increase in frictional force between the transport belt and the absorbent member.